12
START-UP PROCEDURE
Main Burner Adjustment
The gas pressure regulator (integral to the combination gas
control) is adjusted at the factory for average gas conditions.
It is important that gas be supplied to the unit heater in
accordance with the input rating on the serial plate. Actual
input should be checked and necessary adjustments made
after the unit heater is installed. Over-firing, a result of too
high an input, reduces the life of the appliance and increases
maintenance. Under no circumstances should the input exceed
that shown on the serial plate.
Measuring the manifold pressure is done at the outlet pressure
tap of the gas valve. (See Figure 12.2).
To Adjust the Manifold Pressure
1. Move the field installed manual shut-off valve to the “OFF”
position.
2. Remove the 1/8" pipe plug in the pipe tee or gas valve and
attach a water manometer of “U” tube type which is at least
12" high.
3. Move the field installed manual gas shut-off valve to the
“ON” position.
4. Create a high fire call for heat from the thermostat.
5. Determine the correct high fire manifold pressure. For
natural gas 3.5” W.C., for propane gas 10” W.C. Adjust the
main gas pressure regulator spring to achieve the proper
manifold pressure (for location, see the combination gas
control literature supplied with unit).
6. After adjustment, move the field installed manual shut-off
valve to the “OFF” position and replace the 1/8" pipe plug.
7. After the plug is in place, move the field installed manual
shut-off valve to the “ON” position and recheck pipe plugs
for gas leaks with soap solution.
Burner Flame Adjustment
Proper operation provides a soft blue flame with a well-defined
inner core. A lack of primary air will reveal soft yellow-tipped
flames. Excess primary air produces short, well-defined flames
with a tendency to lift off the burner ports. For both natural and
propane gas, the flame may be adjusted by sliding the manifold.
Also, for propane gas, the air shutters can be adjusted to
control the burner flame height. The air shutters
can be accessed by lowering the bottom pan of the unit heater.
Natural Gas Flame Control
Control of burner flames on unit heaters utilizing natural gas is
achieved by resetting the manifold position to either increase
or decrease primary combustion air. Prior to flame adjustment,
operate unit heater for about fifteen minutes. The main burner
flame can be viewed after loosening and pushing aside the gas
designation disc on the back of the unit.
To increase primary air, loosen the manifold mounting screws
and move the manifold away from the burner until the yellow-
tipped flames disappear (see figure 13.1). To decrease primary
air, move manifold closer to the burner until flames no longer lift
from burner ports, but being careful not to cause yellow tipping.
Retighten manifold mounting screws after adjustment.
Propane Gas Flame Control
An optimum flame will show a slight yellow tip. Prior to flame
adjustment, operate furnace for at least fifteen minutes. Loosen
air shutter set screws and move the air shutters away from the
manifold to reduce the primary air until the yellow flame tips
appear (see figure 13.2). Then increase the primary air until
yellow tips diminish and a clean blue flame with a well defined
inner cone appears.
It may also be necessary to adjust the manifold position in
addition to adjusting air shutters to obtain proper flame. Follow
the instructions under "Natural Gas Flame Control" for adjusting
the manifold.
3/4" to 1"
Figure 12.1
Correct Pilot Flame
Figure 12.2
Typical Combination Gas Control
GAS CONTROL KNOB
INLET
PRESSURE TAP
PRESSURE REGULATOR
ADJUSTMENT SCREW
(UNDER CAP SCREW)
OUTLET
PRESSURE
TAP
OUTLET
PILOT TUBING
CONNECTION
PILOT ADJUSTMENT
SCREW
RESET BUTTON
INLET
